The frame and body of a vehicle is constructed with respect to precise geometric relationships as determined by the manufacturer in order that the vehicle have proper driving and road holding properties, as well as accurate exterior design measurement locations. In the manufacture of the vehicle, various sections and beams ultimately comprising the vehicle body and frame are positioned on fixtures or jigs and then the part is welded together to form a unitary structure. Parts are located with respect to the jig or fixture by fixture holes, which are round holes or sockets drilled in the frame so that studs extending upwardly from the fixture or jig extend into the hole. After formation of the body, these holes are often drilled and tapped to form bolt holes for mounting other body parts, such as suspension components, engine carriages and the like.
The jig or fixture is established with respect to an imaginary horizontal reference plane, or datum plane, which extends beneath the vehicle and from which upward dimensions of each fixture point are derived. Further, the fixture points are located longitudinally of the vehicle by establishing one or more zero points along the length of the vehicle. The vehicle fixture holes are also located laterally by establishing a vehicle center line and measuring outwardly. Through measurements originating at the vehicle center line, longitudinal line and datum plane, the location of each point on the vehicle can be established in X, Y and Z coordinate relationship.
The above procedure refers to the process of laying out the vehicle structure when the vehicle is manufactured. By means of a reverse process, the vehicle can be checked in a repair shop to determine if the vehicle body and frame parts are still in their proper relationship or whether there has been dislocation due to various causes, mostly collision and accidents, or even due to out of tolerance manufacturing. Through various procedures, the vehicle body and frame can be checked to blue print specifications.
The process of checking a vehicle to specifications involves referring to a vehicle frame and body book which contains tables or charts showing each vehicle by year and model, identifying critical body and frame measurement points, which normally correspond to fixture holes and joint locations, and applying those measurements to the vehicle to determine the presence of dislocation.
There are various means by which a repairman may recreate, in part or in whole, the reference capabilities of the original fixture or jig on which the car was formed. One such proper method is through the use of the Kansas Jack Laser Alignment System as disclosed in U.S. Pat. No. 4,330,945 and in Kansas Jack Patent Application Ser. No. 764,678, co-pending herewith. Other such systems are exemplified by U.S. Pat. No. 4,490,918 from Continental.
Of critical importance is the re-establishment of the vehicle datum plane, which is an imaginary plane extending under the vehicle and from which all vertical measurements are derived. The vehicle frame and body book indicates the dimensions of the vehicle frame and body parts from the datum plane and by reference to those parts which appear to be undamaged, the datum plane is re-established.
After the datum plane is re-established, the lateral and longitudinal (X and Y) dimensions are re-established by reference to the vehicle frame and body book and by positioning a support structure in the datum plane at the correct X and Y location, such as shown in Patent Application Ser. No. 764,678 filed 8/12/85. The next step is to measure the Z axis dimension, or the vertical height from the datum plane to the fixture hole. Again, that dimension is provided in the vehicle frame and body book. One such method of indicating that dimension is through the use of a laser projector such as shown in Patent Application Ser. No. 764,678 or more crudely by rulers or measuring tapes. The area is often too restricted by other various frame and body parts to permit optical scanning, and hand held measurement bars often do not provide sufficient exactness. Moreover, it is preferable to leave rods in place which extend from the datum plane to the fixture hole, for this arrangement enables the repairman to detect at a glance whether there has been any shift between the established datum plane and the vehicle frame and body after commencing repair procedures. Normally, these repair procedures involve exerting pulls or pushes on various parts of the vehicle through hydraulic or pneumatic rams, and the vehicle may be moved about significantly during the repair process. If the pointers extending from the fixture holes to the datum plane stay in position during this process, it assures the repairman that the datum plane system remains properly positioned with respect to the vehicle frame and body and that the reference remains true.